Lean Muse disturbed mythological king (8)
I believe the answer is:
menelaus
'mythological king' is the definition.
'Menelaus' can be an answer for 'king' (I have seen 'Spartan king' mean 'menelaus' so perhaps 'king' could also mean 'menelaus'). I also know that 'mythological' relates to this answer.
'lean muse disturbed' is the wordplay.
'disturbed' is an anagram indicator.
'lean'+'muse'='leanmuse'
'leanmuse' anagrammed gives 'MENELAUS'.
(Other definitions for menelaus that I've seen before include "Helen of Troy's husband" , "Spartan king" .)